- Lin, Ming-Fu;
- Kochat, Vidya;
- Krishnamoorthy, Aravind;
- Bassman Oftelie, Lindsay;
- Weninger, Clemens;
- Zheng, Qiang;
- Zhang, Xiang;
- Apte, Amey;
- Tiwary, Chandra Sekhar;
- Shen, Xiaozhe;
- Li, Renkai;
- Kalia, Rajiv;
- Ajayan, Pulickel;
- Nakano, Aiichiro;
- Vashishta, Priya;
- Shimojo, Fuyuki;
- Wang, Xijie;
- Fritz, David M;
- Bergmann, Uwe
Photo-induced non-radiative energy dissipation is a potential pathway to induce structural-phase transitions in two-dimensional materials. For advancing this field, a quantitative understanding of real-time atomic motion and lattice temperature is required. However, this understanding has been incomplete due to a lack of suitable experimental techniques. Here, we use ultrafast electron diffraction to directly probe the subpicosecond conversion of photoenergy to lattice vibrations in a model bilayered semiconductor, molybdenum diselenide. We find that when creating a high charge carrier density, the energy is efficiently transferred to the lattice within one picosecond. First-principles nonadiabatic quantum molecular dynamics simulations reproduce the observed ultrafast increase in lattice temperature and the corresponding conversion of photoenergy to lattice vibrations. Nonadiabatic quantum simulations further suggest that a softening of vibrational modes in the excited state is involved in efficient and rapid energy transfer between the electronic system and the lattice.